Frequently in the life of a well additional laterals are needed to properly and more fully produce a formation. Whipstocks are properly positioned in the wellbore and oriented so that the lateral will exit in the proper direction into the target formation. Whipstocks are typically anchored from below and feature a ramp surface in the range of about 3 degrees. As a result the whipstock body is generally fairly long and features a lug near its upper end to allow a window mill to be delivered with it. After proper orientation and anchoring, the window mill is started and it breaks loose from its mounting lug and begins to make the exit or window in the surrounding tubular.
The whipstocks are typically milled from a metal cylinder stock in a process that takes a great deal of time to mill away a ramp that can be over 15 feet long. The resulting rigidity of the whipstock also makes it difficult to manipulate it in deviated wellbores and risks breaking the connection between the window mill and the lug when running in.
Whipstocks have always been made this way. The present invention is a departure from this tradition in that it results in a streamlined manufacturing process that is easier to run in and yet comparably performs to the traditional totally metallic designs. Examples of the whipstocks now in use are illustrated in U.S. Pat. Nos. 6,766,859; 6,497,288; 6,419,024; 6,419,023; 6,419,021; 6,419,012; 6,419,010; 6,386,287; 5,725,060; 5,507,346; 5,499,680; 5,467,820; 5,277,251; 5,199,513 and US Publication Number 2002/0029889. The last reference shows the use of a polymeric coating on the whipstock to protect its metal body and to ease the advancement of a washover tool over the top of the whipstock if it needs to be retrieved.
Apart from the prior art mentioned above, an older technique presents an alternative to milling a whipstock from a metal cylinder. FIGS. 1-3 illustrate the method. A tubular 10 gets a half circumferential cut 12 and two opposed tapered cuts 14 and 16. The cut piece 18 is removed and inverted, as shown in FIG. 3 and welded back into position and the result is a ramp to an opening 20. One disadvantage here is the presence of a piece of the tubular 22 that has an internal diameter 24 which can limit the diameter of the window mill that can fit though and still make the turn on the ramp formed by cut piece 18. FIG. 4 shows a typical milled whipstock 26 that has a retrieval slot 28 and a lug 30 for initial support from a window mill 32. The window is produced in the tubular 34.
The present invention will be more readily understood by those skilled in the art from the discussion of the preferred embodiment and the related drawings and from the claims that define the scope of the invention.